The present invention relates to impurity introduction methods and apparatuses thereof to introduce, in a low temperature range (temperature range of, for example, 250.degree. C. to very low temperature),impurity composed of atoms and molecules to a surface portion of a solid sample such as a semiconductor substrate, and also relates to manufacturing methods of a semiconductor device using such impurity introduction method.
As a technique to introduce impurity to the surface portion of the solid sample, plasma doping method in which impurity is ionized and introduced to a solid with low energy is known as disclosed in, for example, U.S. Pat. No. 4,912,065.
Now, a plasma doping method will be described below as a conventional impurity introduction method with reference to FIG. 8.
FIG. 8 illustrates a schematic structure of an impurity introduction apparatus used for the conventional plasma doping. FIG. 8 shows a vacuum chamber 10, a sample holder 11 provided inside the vacuum chamber 10 for holding a solid sample 12 which is composed of a silicon substrate or the like and to which impurity is introduced, a pressure reducing pump 13 for reducing the pressure inside the vacuum chamber 10, a source gas feed 14 for supplying doping gas including a desired element, such as B.sub.2 H.sub.6, to the vacuum chamber 10, a microwave guide 15 connected to the vacuum chamber 10, a quartz plate 16 provided between the vacuum chamber 10 and the microwave guide 15, and an electromagnet 17 arranged outside the vacuum chamber 10. The microwave guide 15,the quartz plate 16 and the electromagnet 17 constitute plasma generation means. In FIG. 8, a plasma region 18 and a high-frequency power supply 19 connected to the sample holder 11 through a capacitor 20 are also shown.
In the impurity introduction apparatus having the structure above, the doping gas such as B.sub.2 H.sub.6 introduced from the source gas feed 14 is made into plasma by the plasma generation means, and boron ions in the plasma are introduced to the surface portion of the solid sample 12 by the high-frequency power supply 19.
After a metal interconnection layer is formed on the solid sample 12 having thus introduced impurity, a thin oxide film is formed on the metal interconnection layer in the prescribed oxidizing atmosphere. There-after, a gate electrode is formed on the solid sample 12 by a CVD device or the like to obtain, for example, a MOS transistor.
There is a problem that in general the gas including the impurity which becomes electrically active when introduced to the solid sample such as a silicon substrate, such as the doping gas composed of B.sub.2 H.sub.6, is highly dangerous.
In addition, under the plasma doping method, all the substances included in the doping gas are introduced to the solid sample. Taking as an example the doping gas composing B.sub.2 H.sub.6, although only boron is the effective impurity when introduced to the solid sample, hydrogen is also introduced to the solid sample at the same time. If hydrogen is introduced to the solid sample, a lattice defect is undesirably generated at the solid sample during the thermal treatment such as epitaxial growth performed thereafter.
Therefore, the inventors of the present invention have conceived that an impurity solid including the impurity which becomes electrically active when introduced to the solid sample is arranged in the vacuum chamber, and plasma of rare gas as inert or reactive gas is generated in the vacuum chamber and the impurity solid is sputtered by ions of the rare gas so that the impurity is separated from the impurity solid.
FIG. 9. shows a schematic structure of an impurity introduction apparatus used for plasma doping which utilizes an impurity solid including impurity. The elements in FIG. 9 identical to those in FIG. 8 are denoted by the identical numerals and description thereof will not be repeated.
This impurity introduction apparatus is characterized in that the device is provided with a solid holder 22 for holding an impurity solid 21 including impurity such as boron and a rare gas feed 23 for introducing rare gas into the vacuum chamber 10. When gas such as Ar gas is introduced into the vacuum chamber 10 from the rare gas feed 23, the Ar gas is made into plasma by the plasma generation means and boron is sputtered from the impurity solid 21 by the Ar ions in the Ar plasma. Boron thus sputtered is mixed into the Ar plasma to become plasma doping gas and then introduced to the surface portion of the solid sample 12.
However, although it is true that impurity is generated from the impurity solid 21 when the plasma doping is carried out as described above, problems still remain that throughput is not satisfactory because the amount of impurity generated is not sufficient and that the impurity cannot be introduced to the region extremely close to the surface at the surface portion of the solid sample.